Prevention activities targeting substance use and other problem behaviors are becoming increasingly difficult to integrate into school settings due to rising demands for educational testing and accountability for student achievement (Mahoney &Zigler, 2006). Moreover, schools serving children most in need of intervention to help prevent youth substance use and problem behavior often have little additional time and/or resources to focus on student interpersonal skills and adjustment (Kam, Greenberg, &Walls, 2003). With increasing numbers of youth spending time in afterschool settings, community-based afterschool represents a unique and potentially powerful avenue for preventing youth risk for substance use and problem behavior and for promoting youth prosocial behavior and skills. In addition, intervention in afterschool offers the promise for sustainability and broader dissemination of staff development approaches using fairly economic consultation and training approaches. Clearly, establishing effective practices in afterschool programs has important public health implications (Kellam, Koretz, &Moscicki, 1999). Although systematic research focusing on prevention and promotion in afterschool has only recently begun to emerge, initial findings suggest that structured and supervised settings are associated with risk prevention for substance use and other problem behavior and with enhanced youth bonding to school, academic achievement, social skills, positive self-perceptions, and identity (Belgrave et al., 2000;Durlak &Weissberg, 2007;Gottfredson et al., 2004;Larson, 2000;Lerner, 1995, 2005). This project proposes a "science-migration" study, that is, testing a school-based approach found to have longitudinal effects upon substance abuse, aggression, and internalizing behavior in afterschool programs. Over the past 40 years since its inception, the Good Behavior Game (GBG) has emerged as an effective approach for reducing behavior problems and substance abuse among youth (Baer et al., 1968;Furr-Holden et al., 2004;Ialongo et al., 1999). This randomized efficacy study of afterschool programs will examine the effects of GBG on substance use and other problem behaviors and on positive behaviors in youth. The latter is particularly significant because previous research has demonstrated that shared norms, supportive relationships with adults and association with conventional peers are all factors related to reduced problem behavior and substance use (Ayers et al., 1999;Elliott, Huizinga, &Menard, 1989;Huizinga et al., 2003), and are specifically cultivated through the cooperative game. The project will involve approximately 72 afterschool programs, primarily in Pennsylvania, from urban and rural locales with participants of diverse racial-ethnic backgrounds (e.g., African American, Latino, and White) randomly assigned to receive program support and coaching or treatment as usual. The study, designed to advance research and practice in prevention of substance use and aggression in community-based afterschool, will examine intervention outcomes, moderators of program effectiveness, and hypothesized mechanisms of change. PUBLIC HEALTH RELEVANCE: Substance abuse and use has important public health relevance and affects all racial and ethnic groups. Additionally, substance abuse is often accompanied by other problem behavior among youth, including lower academic achievement, violence, and aggression (Henry &Huizinga, 2007;Elliott, Huizinga &Menard, 1989). Furthermore, substance abuse has costs. In 2007 the Substance Abuse and Mental Health Services Administration allocated $24 million to treat targeted populations suffering from substance abuse related issues (SAMHSA, 2007). There are also costs in loss human potential and incarceration for comorbid delinquency. Though substance abuse affects a wide population, ethnic minority youth are more likely to be incarcerated on drug related charges (Blumstein &Wallman, 2000). Addressing substance abuse and accompanying disparities meets the overarching goals of the Healthy People 2010 initiative, whose goals are to increase quality of life and longevity as well as eliminating health disparities among Americans (Office of Disease Prevention, 2008).